Java: making List from primitive array using Stream API

问题

I'm trying to make a List from a primitive array

int[] values={4,5,2,3,42,60,20};
List<Integer> greaterThan4 =
Arrays.stream(values)
        .filter(value -> value > 4)
        .collect(Collectors.toList());

But the last function collect gives me an error because it wants other arguments. It wants 3 arguments Supplier, ObjIntConsumer and BiConsumer.

I don't understand why it wants 3 arguments when I have seen different examples that just use collect(Collectors.toList()); and get the list.

What I'm doing wrong?

回答1:

Yes this is because Arrays.stream returns an IntStream. You can call boxed() to get a Stream<Integer> and then perform the collect operation.

List<Integer> greaterThan4 = Arrays.stream(values)
                                   .filter(value -> value > 4)
                                   .boxed()
                                   .collect(Collectors.toList());

回答2:

You can change int[] values={4,5,2,3,42,60,20}; to Integer[] values={4,5,2,3,42,60,20}; because currently you are passing an array of primitive type(int) but should you pass array of object i.e. Integer

回答3:

You're using an array of primitives for one thing, not Integer. I suggest you use Arrays.asList(T...) like

Integer[] values={4,5,2,3,42,60,20};
List<Integer> al = new ArrayList<>(Arrays.asList(values));

来源：https://stackoverflow.com/questions/27572859/java-making-list-from-primitive-array-using-stream-api